U.S. patent application number 10/566893 was filed with the patent office on 2006-08-10 for seafloor-surface coupling device comprising a flexible, leak-tight connection between a riser and a float.
Invention is credited to Michael Gassert, Olivier Moog, Alain Skraber, Yves Stassen.
Application Number | 20060177276 10/566893 |
Document ID | / |
Family ID | 34073115 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060177276 |
Kind Code |
A1 |
Stassen; Yves ; et
al. |
August 10, 2006 |
Seafloor-surface coupling device comprising a flexible, leak-tight
connection between a riser and a float
Abstract
The present invention relates to a bottom-to-surface connection
device comprising at least one undersea pipe or riser (1, 1a-1b)
capable of including a single float (2, 2.sub.1-2.sub.7), said
float being connected at its bottom end to a junction device (8)
creating a leaktight flexible joint between the bottom end of the
float (2) and said riser (1a), the connection device being
characterized in that said junction device (8) is interposed
between and secured to a bottom portion (1a) of the riser going
down to the sea bottom and a top portion of the riser passing
through said float and rising to the surface, said junction device
(8) comprising at least one first laminated abutment in the form of
a body of revolution having a plurality of elastomer layers
defining surfaces of revolution that are frustoconical in shape or
ellipsoidal in section.
Inventors: |
Stassen; Yves; (Issy Les
Moulineaux, FR) ; Gassert; Michael; (Levallois
Perret, FR) ; Moog; Olivier; (Mulhouse, FR) ;
Skraber; Alain; (Masevaux, FR) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE
551 FIFTH AVENUE
SUITE 1210
NEW YORK
NY
10176
US
|
Family ID: |
34073115 |
Appl. No.: |
10/566893 |
Filed: |
July 23, 2004 |
PCT Filed: |
July 23, 2004 |
PCT NO: |
PCT/FR04/01968 |
371 Date: |
February 1, 2006 |
Current U.S.
Class: |
405/224.3 |
Current CPC
Class: |
E21B 17/012
20130101 |
Class at
Publication: |
405/224.3 |
International
Class: |
E21B 17/01 20060101
E21B017/01 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2003 |
FR |
0309798 |
Claims
1. A bottom-to-surface connection device comprising at least one
undersea pipe or riser (1, 1a-1b) including at least one float and
possibly including only one float (2, 2.sub.1-2.sub.7), said float
being connected at its bottom end to a junction device (8) creating
a leaktight flexible joint between the bottom end of the float (2)
and said riser (1a), the connection device being characterized in
that said junction device (8) is interposed between and secured to
a bottom portion (1a) of the riser going down to the sea bottom and
a top portion (1b) of the riser passing through said float and
rising to the surface, said junction device (8) comprising at
least: a first forged body of revolution (22) secured to the top
end of said bottom portion (1a) of the riser, and forming an
internal tubular duct section (22.sub.3) having substantially the
same diameter as said bottom portion of the riser; and a second
forged body of revolution (24) secured to the bottom end of said
top portion (1b) of the riser, and forming an internal tubular duct
section (24.sub.4) having substantially the same diameter as said
top portion (1b) of the riser; said first and second forged bodies
(22, 24) being interconnected in flexible and leaktight manner by
at least a first flange (23) in the form of a body of revolution
secured in leaktight and reversible manner to said second forged
body (24) and connected to said first forged body (22) by at least
a first laminated abutment (30) in the form of a body of
revolution, comprising a plurality of elastomer layers interposed
between rigid reinforcements preferably made of metal defining
surfaces of revolution having the same axis as the common
longitudinal axis of revolution ZZ' of said first and second forged
bodies (22, 24) and said first flange (23, 23a-23b), said surfaces
of revolution being frustoconical in shape or skew surfaces, such
as surfaces of sections that are ellipsoidal or parabolic or
hyperbolic or preferably spherical in shape.
2. A bottom-to-surface connection device according to claim 1,
comprising an undersea pipe or riser (1, 1a-1b) tensioned by at
least one float (2, 2.sub.1, 2.sub.7) constituted by a can
presenting a cylindrical casing (20) surrounding said pipe (1b)
coaxially, located on the high underwater portion of said pipe (1,
1a-1b), said pipe (1, 1a, 1b) preferably being held and guided by a
surface guide device (4, 6) located at a floating support (10) and
including a said junction device (8) for said can (20), the
connection device being characterized in that: said first forged
body (22) presents in its top portion an outer first surface of
revolution (22.sub.1) that is preferably frustoconical in shape or
of ellipsoidal section; and said second forged body of revolution
(24) secured to the bottom end of said top portion (1b) of the
riser, preferably by welding (24a), presents in its bottom portion
a bottom first surface (24.sub.1); and said first flange (23,
23a-23b) presents: an inner first surface of revolution (23.sub.1)
of frustoconical shape or of ellipsoidal section, said inner first
surface (23.sub.1) of the first flange (23, 23a-23b) and said outer
first surface (22.sub.1) of the first forged body (22) being
situated facing each other and co-operating elastically and in
leaktight manner via a said first laminated abutment (30) in the
form of a body of revolution that is frustoconical in shape or
respectively of ellipsoidal section, comprising a plurality of
layers of elastomer sandwiched between reinforcing sheets of rigid
material, in particular steel sheets, bonded to said inner first
surface (23.sub.1) and said outer first surface (22.sub.1) thus
bonding together said first flange (23, 23a-23b) and said first
forged body (22); and at least a portion of a top surface
(23.sub.2) of said first flange (23, 23a-23b) co-operating in
leaktight manner, preferably via at least one O-ring (28), with
said bottom surface (24.sub.1) of said second forged body of
revolution (24), said top surface portion (23.sub.2) of said first
flange (23, 23a-23b) and said top surface (24.sub.1) of said second
forged body (24) being secured to each other in leaktight and
reversible manner, preferably by bolting (27); and said outer
casing (20) of the float (2) being secured to a top surface
(24.sub.2) of said second forged body (24) or to a top surface
(21.sub.1) of a second flange (21) in the form of a body of
revolution having a bottom surface (21.sub.2), itself bonded in
leaktight and reversible manner, preferably by bolting (25) and via
at least one O-ring (26), to a portion of said top surface of
revolution (23.sub.2) of said first flange (23, 23a-23b).
3. A device according to claim 1 or claim 2, characterized in that
said second forged body of revolution (24) includes in its bottom
portion an outer second surface (24.sub.3) of frustoconical shape
or preferably of ellipsoidal section, and said outer second surface
of revolution (24.sub.3) is situated facing and co-operates
elastically and in leaktight manner with an inner second surface of
revolution (22.sub.2) of frustoconical shape or respectively of
ellipsoidal section, said inner second surface (22.sub.2) being
situated in the top portion of said second forged body (22), and
said inner second surface (22.sub.2) being connected to said outer
second surface (24.sub.3) via a second laminated abutment (31) in
the form of a body of revolution constituted by a plurality of
elastomer layers sandwiched between rigid reinforcing sheets, in
particular of steel, that are frustoconical in shape or
respectively of ellipsoidal section, and that are bonded to said
outer second surface (24.sub.3) and to said inner second surface
(22.sub.2).
4. A device according to claim 2 or claim 3, characterized in that
said first abutment (30) and where appropriate said second abutment
(31), said outer first surface (22.sub.1) of the first forged body
(22), said inner first surface (23.sub.1) of the first flange (23,
23a-23b), and, where appropriate said outer second surface of
revolution (24.sub.3) of the second forged body (24), and said
inner second surface of revolution (22.sub.2) of the first forged
body (22) are all frustoconical in shape about the same said axis
of revolution ZZ', with an angle of the apex .beta. lying in the
range 30.degree. to 80.degree., preferably in the range 40.degree.
to 70.degree., the apexes of the various frustoconical surfaces
being situated below said frustoconical surfaces, and the various
frustoconical surfaces either sharing a common angle at the apex
.beta. or a common apex C.
5. A device according to any one of claims 1 to 3, characterized in
that said first abutment (30), and, where appropriate said second
abutment (31), said outer first surface (22.sub.1) of the first
forged body (22), said inner first surface (23.sub.1) of the first
flange (23, 23a-23b), and, where appropriate said outer second
surface of revolution (24.sub.3) of the second forged body (24),
and said inner second surface of revolution (22.sub.2) of the first
forged body (22) are all of ellipsoidal section, preferably of
spherical section, all being substantially centered on the common
point C situated above said surfaces and on said axis of revolution
ZZ'.
6. A device according to any one of claims 1 to 5, characterized in
that said first and second forged bodies (22, 24) and said first
flange (23, 23a-23b) define a first internal chamber (40) which
preferably co-operates with pressure sensor means (41, 42) for
monitoring the pressure inside said chamber (40).
7. A device according to claim 6, characterized in that said first
chamber (40) is defined by the top portion of said first forged
body (22) and by the free portions of said bottom surface of
revolution (24.sub.1) of said second forged body (24), said concave
inner first surface of revolution (23.sub.1) of said first flange
(23, 23a-23b), and said convex outer second surface of revolution
(24.sub.3) of said second forged body (24).
8. A device according to any one of claims 2 to 7, characterized in
that said outer casing (20) of the float (2) is secured to an
internal second pipe (3) of greater diameter than said riser (1,
1b), said internal second pipe (3) preferably being a reinforced
pipe of thickness greater than said riser (1), and in that it
includes a said second flange (21) in the form of a body of
revolution to which the bottom end of said outer casing (20) of the
float (2) and the bottom end of said internal second pipe (3) are
secured, preferably by welding (21a, 21b), said second flange (21)
surrounding said second forged body (24) so that a second inner
chamber (45) is defined by an inner surface of revolution
(21.sub.3) of said second flange (21) having the same axis of
revolution ZZ', by said top surface of revolution (24.sub.2) of
said second forged body (24), by the cylindrical outer surface
(1.sub.1) of said top portion (1b) of the riser and the cylindrical
inside surface (3.sub.1) of said internal second pipe (3), and by a
closure flange (5) at the top ends of said internal second pipe (3)
and of said top portion (1b) of the riser, said second chamber (45)
preferably co-operating with means for monitoring the pressure (47,
48) inside said second chamber (45).
9. A device according to any one of claims 2 to 8, characterized in
that said top surface peripheral (23.sub.2) of the first flange
(23, 23a-23b) and said bottom surface (24.sub.1) of the second
forged body (24), and where appropriate said bottom surface
(21.sub.2) of said second flange (21), are annular plane
surfaces.
10. A device according to claim 8 or claim 9, characterized in that
said internal second pipe (3) extends above said float (2),
preferably in the form of a reinforced pipe of thickness greater
than said riser (1) which it surrounds, and preferably a holding
and guide device (4, 6) serves to guide said internal second pipe
(3) relative to said floating support (10).
11. A device according to any one of claims 1 to 10, characterized
in that the top end of the float (2) is secured to the top portion
(1b) of the riser (1) or of said internal second pipe (3) via a
rigid junction (8.sub.1)
12. A device according to any one of claims 1 to 11, characterized
in that said float (2) is a single float extending over a length of
40 m to 100 m in order to confer buoyancy enabling the entire
bottom-to-surface connection to be tensioned, said float (2)
preferably being made up of segments that are assembled to one
another, each being constituted by a cylindrical box, which boxes
are preferably individually sealed (2.sub.1, 2.sub.7), and secured
mechanically to one another in the longitudinal direction ZZ'.
13. A device according to any one of claims 1 to 11, characterized
in that the buoyancy of said undersea pipe (1) is provided by said
float without adding any additional tensioning system that is
secured to the floating support (10).
14. A device according to any one of claims 1 to 13, characterized
in that it includes stabilizer means (60, 61) in the bottom portion
(2.sub.7) of the float (2) having the effect of increasing the mass
of water it entrains when it moves, or lowering the center of
gravity of the top portion of the pipe in the float (2).
15. A device according to claim 14, characterized in that a
stabilizer means comprise a helical ramp (61) surrounding the
bottom portion (2.sub.7) of said float (2) close to its bottom
end.
16. A device according to claim 14, characterized in that a
stabilizer means comprises an additional peripheral mass (60)
situated around the bottom portion (2.sub.7) of the float (2).
17. A device according to any preceding claim, characterized in
that said first flange (23) comprises two portions (23a-23b) in
which the first portion (23a) is a body of revolution including
said inner first surface (23.sub.1), and said second portion (23b)
is a peripheral flange including said top surface (23.sub.2), said
second portion (23b) being secured in leaktight and reversible
manner to said first portion (23a) via at least one O-ring (29) by
securing in leaktight and reversible manner said top surface
peripheral (23.sub.2) of the first flange (23) to said bottom
surface (24.sub.1) of said forged second body (24).
Description
[0001] The present invention relates to the known field of
bottom-to-surface connections of the type comprising a vertical
undersea pipe referred to as a "riser" connecting the sea bottom to
the surface, preferably going to a floating support installed on
the surface.
[0002] Once the depth of water becomes large, a production field,
and in particular an oil field, is generally worked from a floating
support. The floating support generally includes anchor means for
keeping it in position in spite of the effects of currents, winds,
and swell. It also generally includes means for storing and
processing oil and means for off-loading to off-loading tankers.
Such floating supports are generally referred to as floating
production storage off-loading (FPSO) supports. Numerous variants
have been developed such as so-called SPARS which are long floating
cigars held in position by catenary anchoring, or indeed "TLPs"
which are platforms having tensioned anchor lines, said lines
generally being vertical.
[0003] Wellheads are generally distributed over the entire field,
and production pipes together with lines for injecting water and
control cables are placed on the sea bottom converging on a fixed
location, with the floating support being positioned vertically
thereabove on the surface.
[0004] Some wells are situated vertically beneath the floating
support and the inside of the well is then directly accessible from
the surface. Under such circumstances, the wellhead fitted with its
"Christmas tree" can be installed on the surface, on board the
floating support. It is then possible from a derrick installed on
said floating support to perform all of the drilling, production,
and maintenance operations required on the well throughout its
lifetime. The wellhead is then said to be "dry".
[0005] In order to keep the riser fitted with its dry wellhead
substantially in its vertical position, it is necessary to exert
upward traction thereon, which can be applied either by a
tensioning system using cables and winches or hydraulic actuators
installed on the floating support, or else by floats distributed
along the riser and installed at various depths, or indeed by using
a combination of those two techniques.
[0006] The riser as tensioned by these floats is guided, preferably
relative to the floating support, by roller guides situated in a
plane, preferably a single plane, enabling a riser to be held and
guided relative to the floating support. Cable tensioning means
acting as guide means can also be used.
[0007] FR 2 754 021 discloses a guide device for a riser provided
with floats at its head end, the device including wheels enabling
the riser to slide vertically, and also enabling it to turn about a
horizontal axis so as to guide its horizontal displacements, so
that horizontal translation movements of the riser substantially
follow those of the floating supports. FR 99/10417 and
WO/2001-11184 also disclose an improved guide device having wheels
and friction skids disposed radially around the pipe. That device
for holding and guiding the portion of a vertical riser that is
underwater and near the surface, in particular within a drilling
bay, serves to minimize the reaction forces between said riser and
the support structure secured to the barge. Finally, various guide
systems are known that involve tensioning by cable means.
[0008] Since the underwater depth of certain oil fields exceeds
1500 meters (m), and can be as great as 3000 m, the weight of
risers over such depths requires forces to be used for holding them
in position that can reach or exceed several hundreds of (metric)
tonnes. "Can_type" buoyancy elements are used that are added to
underwater structures, mainly to risers connecting ultra-great
depths (1000 m-3000 m) to the surface. The underwater pipe then
consists in a rising column having an underwater pipe assembled to
at least one float comprising a coaxial can surrounding said pipe
with said pipe passing therethrough.
[0009] The floats in question are of large dimensions, and in
particular they have a diameter of more than 5 m, a length of 10 m
to 20 m, and possess buoyancy that can be as great as 1000 tonnes,
and in general they are disposed as a string one beneath
another.
[0010] The float and the pipe are subjected to the effects of swell
and current, but since they are connected to the FPSO at the
surface, they are also indirectly subjected to the effects of wind.
This gives rise to lateral and vertical movements that are large
(several meters) for the riser-float-barge combination,
particularly in the zone that is subjected to swell. These
movements generate large differential forces between the riser and
the float. In addition, the bending applied to the riser leads to
bending moments that are extremely large in the zone where there is
a change in second moment of area, as arises whenever there is a
connection between the riser and a float.
[0011] In order to minimize the forces generated by current and
swell and acting on the riser-float combination, floats are
generally circular and are installed coaxially around the
riser.
[0012] In addition, floats are generally secured to the riser in
such a manner that the riser-float connection provides sealing to
said float so that it can confine a filler gas. The solution that
is commonly used consists in embedding the float in the riser by
welding, both at the top and at the bottom of the riser. Large
amounts of reinforcement are added to ensure that the connection is
sufficiently strong.
[0013] At such a connection between the riser and a float, the
second moment of area changes considerably on passing from the
section of the riser to the section of the float.
[0014] These large variations in second moment of area lead to
stresses being unevenly distributed, thereby generating very
localized zones in which stresses can become unacceptable and can
lead either to phenomena of sudden rupture, or else to phenomena of
fatigue that in turn lead to cracks appearing, followed by
collapse. These localized stresses require transition pieces to be
used to reinforce the weak zone, said pieces generally being
conical in shape and of large dimensions, and being referred to as
"tapered joints". In some circumstances, these pieces can be as
much as 10 m long, and even under the best of circumstances they
require the use of very high performance steels. However, it is
often necessary to make use of titanium which is 5 to 10 times as
expensive as the best steels. In addition, such pieces are
generally complex in shape and they need to be made with extremely
high quality so as to provide the expected service throughout the
lifetime of the equipment, which lifetime can commonly exceed 25
years.
[0015] U.S. Pat. Nos. 3,952,526 and 3,981,357 disclose junction
systems between float-tanks and risers, in which use is made of
parts made of elastomer material.
[0016] Those buoyancy systems make it possible to reduce the
tensioning system situated on board the floating support, and they
are generally distributed over a major fraction of the water depth,
and in addition they present small buoyancy, generally a few
hundreds of kilograms (kg) or possibly one or two tonnes.
[0017] The junctions are situated in the top portions of the
floats, with the bottom portions of the floats generally being
open. Such devices can transfer loads corresponding to lightening
only a short length of the pipe, but they are not suitable for
floats that are intended to support a very great length of riser,
e.g. 500 m to 1000 m or even more, either alone or with the help of
additional tensioning systems secured to the floating support,
where such lengths are to be found in very deep offshore oil
fields, i.e. at depths of more than 1000 m. The buoyancy needed to
achieve tensioning solely by means of floats requires considerable
forces to be transferred vertically and transversely, and said
vertical forces, when applied to the head of the riser, can reach
several hundreds of tonnes, and can in particular lie in the range
300 tonnes to 500 tonnes.
[0018] In WO/2001-04454 in the name of the Applicant, there is
disclosed a novel type of junction between the riser and the can
that serves to support and transfer high loads, while mitigating
the drawbacks of the above-mentioned floats assembled around said
pipe by the pipe being embedded therein.
[0019] Those (riser-float) junction means are simple, flexible, and
mechanically reliable, and they reduce the phenomena of fatigue and
wear due to the stresses acting on the junction which is subjected
to loads of several hundreds of tonnes.
[0020] More particularly, patent WO/2001-04454 in the name of the
Applicant describes a string of floats surrounding a vertical
riser, each of said floats being fitted at at least one of its ends
with a flexible joint comprising laminated abutments serving not
only to provide sealing and to transfer loads, but also to decouple
the second moment of area between the structures of said float and
of said riser, so that there is practically no longer any zone in
which stresses are concentrated at the transition between said
float and said riser, thereby making it possible to reduce the
complexity of the structure of the connection and also its own
weight, thus significantly increasing the efficiency of the float,
i.e. its buoyancy compared with its own weight.
[0021] Still more precisely, WO/2001-04454 describes junction
devices between the riser and the float that comprise laminated
abutments made up of layers of elastomer sandwiched between rigid
reinforcements, being supported by plates comprising a first plate
secured to the pipe and a second plate secured to the float, with
said rigid reinforcements and elastomer layers being:
[0022] either in the form of superposed washers;
[0023] or in the form of tubes or cylinders that are coaxial and
adjacent.
[0024] In WO/2001-04454, the bottom-to-surface connection is thus
continuous in the zone where the float is installed, and the
flexible junction serves to decouple the second moment of area of
said float from that of said riser.
[0025] Current acts over the entire height of the riser, from the
sea bottom up to its surface, but swell acts only in a zone close
to the surface and decreases in substantially exponential manner so
as to become practically zero at a depth of about 80 m to about 120
m. Thus, when using a string of mutually independent floats as
described in WO/2001-04454, the top floats are subjected to
considerable forces both laterally and vertically since the effects
of swell are very large in zones close to the surface, while the
bottom floats are subjected to much less stress. The unit
dimensions of the floats are limited since they must be capable of
being handled on board the barge and then introduced into the
derrick in order to be lowered through the drilling bay. Thus, in
very great depth, e.g. of 2000 m to 3000 m, the weight of the riser
is such that a large number of floats is required, e.g. four or
five floats presenting total buoyancy of 400 tonnes to 500 tonnes
and extending over a height of about 100 m.
[0026] Each of the floats needs to be fitted with laminated
abutments so as to minimize the transfer of stresses to the
vertical riser which constitutes a highly critical element of the
bottom-to-surface connection since it must be capable not only of
withstanding very high tensions, but also it must be capable of
withstanding the bursting pressure created by the fluid it
transports, and also the implosion pressure created by the sea
water.
[0027] This buoyancy, which is distributed as a multitude of
independent floats, requires numerous laminated abutments to be
used, each being of high cost. In addition, swell creates
differential forces between pairs of adjacent floats, which forces
are in addition to the considerable forces to which the riser is
subjected at each discontinuity between the riser and a float.
[0028] It is thus desired to minimize the number of floats, but
when the floats take on large dimensions, the transition zone
between the bottom end of the float and the riser concentrates
considerable horizontal thrust forces, thereby requiring said riser
to be reinforced by a transition piece constituted by a conical
forging of great length that is very difficult to fabricate and
therefore very expensive, since it is generally made of very high
performance metal, such as titanium. When there is only one float,
it needs to be enormous when the depth of water is large, and the
risk of failure associated with the transition piece then becomes
very high and therefore unacceptable because of the high risk of
pollution in the event of said bottom-to-surface connection failing
or rupturing.
[0029] Furthermore, the entire riser behaves like a tensioned cord
between the sea bottom and the point situated on the axis of the
guide system relative to the floating support, and this leads to
vibratory phenomena of the guitar-pendulum type. Water moving in
the depth of the water creates drag effects on the structure of the
riser and its floats, thereby generating large forces in varying
directions, together with vibratory phenomena created by turbulence
in the moving water separating from the riser.
[0030] Patent WO/2001-53651 in the name of the Applicant describes
a device for stabilizing a bottom-to-surface connection of the type
comprising a riser tensioned by a float, said tensioned riser being
guided at a surface support, preferably in a single plane. Said
stabilization device serves to avoid vibratory phenomena of the
guitar-pendulum type appearing, thus avoiding localized
accumulations of fatigue appearing in the steel as are usually to
be encountered in the transition zone between the bottom of the
float and the portion of the riser situated immediately below said
float, said fatigue phenomena leading rapidly to cracking and then
to rupture of the installation.
[0031] Nevertheless, that stabilizer device does not make it
possible to avoid having recourse to reinforced transition pieces,
generally conical forgings of steel or titanium, where titanium
presents particularly high performance in terms of resistance to
fatigue, but is particularly expensive because of its raw material
cost and its difficulty of manufacture.
[0032] The object of the present invention is thus to provide a
novel type of junction between a riser and a float that improves
the fatigue behavior in the zone that is the most highly stressed
at the bottom end of the float, thereby reducing the probability of
a phenomenon of the riser and/or the junction means being destroyed
at said level.
[0033] Another object of the present invention is to provide a
novel type of junction between a riser and a float that is simple
to put into place when installing a bottom-to-surface connection
device.
[0034] Another object of the present invention is to provide a
novel type of junction between a riser and a float that makes it
possible to avoid having recourse to a reinforced transition piece
in the zone between the bottom end of the float and the portion of
the riser that is situated immediately therebelow.
[0035] Another object of the present invention is to provide the
buoyancy of a bottom-to-surface connection device using a single
float.
[0036] Another object of the present invention is to provide a
novel type of junction between a riser and a float that makes it
possible to monitor any possible cracking and thus to monitor loss
of sealing from the riser in said junction zone and/or in the
junction means themselves.
[0037] To do this, the present invention provides a
bottom-to-surface connection device comprising at least one
undersea pipe or riser including at least one float and possibly
including only one float, said float being connected at its bottom
end to a junction device creating a leaktight flexible joint
between the bottom end of the float and said riser, the connection
device being characterized in that said junction device is
interposed between and secured to a bottom portion of the riser
going down to the sea bottom and a top portion of the riser passing
through said float and rising to the surface, said junction device
comprising at least:
[0038] a first forged body of revolution secured to the top end of
said bottom portion of the riser, and forming an internal tubular
duct section having substantially the same diameter as said bottom
portion of the riser; and
[0039] a second forged body of revolution secured to the bottom end
of said top portion of the riser, and forming an internal tubular
duct section having substantially the same diameter as said top
portion of the riser;
[0040] said first and second forged bodies being interconnected in
flexible and leaktight manner by at least a first flange in the
form of a body of revolution secured in leaktight and reversible
manner to said second forged body and connected to said first
forged body by at least a first laminated abutment in the form of a
body of revolution, comprising a plurality of elastomer layers
interposed between rigid reinforcements preferably made of metal
defining surfaces of revolution having the same axis as the common
longitudinal axis of revolution ZZ' of said first and second forged
bodies and said first flange, said surfaces of revolution being
frustoconical in shape or skew surfaces, such as surfaces of
sections that are ellipsoidal, preferably spherical, or parabolic
or hyperbolic or in shape.
[0041] The axis of symmetry and the axis of revolution ZZ' coincide
when the junction device is in the rest position.
[0042] The term "surface of revolution of ellipsoidal, parabolic,
or hyperbolic section" is used herein to mean a surface of
revolution that is respectively ellipsoidal, parabolic, or
hyperbolic and that is defined by two parallel section planes
perpendicular to said axis of revolution ZZ'.
[0043] By means of the structure of the junction device, and in
particular the shape of the layers of elastomer in said laminated
abutments that are frustoconical or spherical in shape, the hinged
connection of the present invention makes pivoting movements
possible in association with a self-centering effect. As a result,
overall, the stresses and the deformations generated at said
laminated abutments and said forged bodies are minimized and make
it possible to maintain or to restore a substantially aligned
position for the top and bottom portions of said riser.
[0044] Thus, the junction device of the present invention is
suitable for providing the junction between the riser and a single
large tensioning float in a manner that is reliable, whereas the
junction devices described in WO/2001-04454 are suitable only for
providing a junction between the riser and small floats disposed as
a string.
[0045] More particularly, a bottom-to-surface connection device of
the invention comprises an undersea pipe or riser tensioned by at
least one float constituted by a can presenting a cylindrical
casing surrounding said pipe coaxially, located on the high
underwater portion of said pipe, said pipe preferably being held
and guided by a surface guide device located at a floating support
and including a said junction device for said can, the connection
device being characterized in that:
[0046] said first forged body presents in its top portion an outer
first surface of revolution that is preferably frustoconical in
shape or of ellipsoidal section; and
[0047] said second forged body of revolution secured to the bottom
end of said top portion of the riser, preferably by welding,
presents in its bottom portion a bottom first surface; and
[0048] said first flange presents: [0049] an inner first surface of
revolution of frustoconical shape or of ellipsoidal section, said
inner first surface of the first flange and said outer first
surface of the first forged body being situated facing each other
and co-operating elastically and in leaktight manner via a said
first laminated abutment in the form of a body of revolution that
is frustoconical in shape or respectively of ellipsoidal section,
comprising a plurality of layers of elastomer sandwiched between
reinforcing sheets of rigid material, in particular steel sheets,
bonded to said inner first surface and said outer first surface
thus bonding together said first flange and said first forged body;
and [0050] at least a portion of a top surface of said first flange
co-operating in leaktight manner, preferably via at least one
O-ring, with said bottom surface of said second forged body of
revolution, said top surface portion of said first flange and said
top surface of said second forged body being secured to each other
in leaktight and reversible manner, preferably by bolting; and
[0051] said outer casing of the float being secured to a top
surface of said second forged body or to a top surface of a second
flange in the form of a body of revolution having a bottom surface,
itself bonded in leaktight and reversible manner, preferably by
bolting and via at least one O-ring, to a portion of said top
surface of revolution of said first flange.
[0052] Preferably, said top and bottom surfaces of said first and
second flanges and of said second forged body are annular plane
surfaces or surfaces of revolution, said first and second forged
bodies and said first flange, and where appropriate said second
flange, and said annular plane surfaces or surfaces of revolution
all have a common axis of symmetry or of revolution ZZ' when in the
rest position.
[0053] Still more particularly, said second forged body of
revolution includes in its bottom portion an outer second surface
of frustoconical shape or preferably of ellipsoidal section, and
said outer second surface of revolution is situated facing and
co-operates elastically and in leaktight manner with an inner
second surface of revolution of frustoconical shape or respectively
of ellipsoidal section, said inner second surface being situated in
the top portion of said second forged body, and said inner second
surface being connected to said outer second surface via a second
laminated abutment in the form of a body of revolution constituted
by a plurality of elastomer layers sandwiched between rigid
reinforcing sheets, in particular of steel, that are frustoconical
in shape or respectively of ellipsoidal section, and that are
bonded to said outer second surface and to said inner second
surface.
[0054] In a first particular variant, said first abutment and where
appropriate said second abutment, said outer first surface of the
first forged body, said inner first surface of the first flange,
and, where appropriate said outer second surface of revolution of
the second forged body, and said inner second surface of revolution
of the first forged body are all frustoconical in shape about the
same said axis of revolution ZZ', with an angle of the apex .beta.
lying in the range 30.degree. to 80.degree., preferably in the
range 40.degree. to 70.degree., the apexes of the various
frustoconical surfaces being situated below said frustoconical
surfaces, and the various frustoconical surfaces either sharing a
common angle at the apex .beta. or a common apex C.
[0055] It will be understood that either said truncated cones flare
upwards and converge substantially on a single point C, in which
case they present an angle at the apex .beta. that varies from one
cone to another, or else they have the same angle at the apex, with
their apexes then being distributed substantially along said axis
of revolution ZZ'.
[0056] In a preferred second particular variant, said first
abutment, and, where appropriate said second abutment, said outer
first surface of the first forged body, said inner first surface of
the first flange, and, where appropriate said outer second surface
of revolution of the second forged body, and said inner second
surface of revolution of the first forged body are all of
ellipsoidal section, preferably of spherical section, all being
substantially centered on the common point .largecircle. situated
above said surfaces and on said axis of revolution ZZ'.
[0057] By means of its makeup interposed between the two riser
portions and comprising various forged bodies and flanges secured
to one another, the junction device of the present invention is
particularly easy to put into place when installing the
bottom-to-surface connection device.
[0058] Furthermore, and above all, the junction device of the
present invention provides a leaktight flexible joint that is
particularly effective, since during movement of the float
associated with the riser due to swell and current, the articulated
connection between the float and the riser can accommodate pivoting
while keeping the bottom portion of the riser in tension. The
preferably spherical shape of said first laminated abutments in
accordance with the invention has a self-centering effect, and the
entire tensioning force created by the float (which can exceed 500
tonnes) is transferred to the riser in a manner that is uniformly
distributed merely by deformation. When the connection device takes
on an angle .alpha., the deformation in the laminated abutments
remains substantially uniform and the stresses generated within the
various components of the laminated abutments also remain
substantially uniform.
[0059] Said angle .alpha. that results from the laminated abutment
deforming preferably lies in the range 0.degree. to 5.degree..
[0060] It will be understood that when it is stated in the present
application that the axes of revolution of the various components
and surfaces are the same, it should be understood that the axes of
revolution of said first and second forged bodies coincide and
likewise the axes of revolution of the flanges and of the surfaces
of revolution also coincide, providing the structure is at rest,
i.e. when there is no bending, as is made possible by said flexible
joint device of the invention.
[0061] Said laminated abutment enhances the self-centering effect
and the load take-up effect of the first laminated abutment, while
also enhancing the primary sealing function so that in an
advantageous embodiment, said first and second forged bodies and
said first flange define between them a first internal chamber
which preferably co-operates with means for monitoring the pressure
inside said chamber.
[0062] More precisely, said first chamber is defined by the top
portion of said first forged body and by the free portions of said
bottom surface of revolution of said second forged body, said
concave inner first surface of revolution of said first flange, and
said convex outer second surface of revolution of said second
forged body.
[0063] Said inner chamber fitted with pressure monitoring means
makes it possible to monitor degradations and/or losses of sealing
through one of the laminated abutments, or indeed cracking in one
of the components of the junction device including the leaktight
joint, and/or the riser. When the pressure in said chamber varies,
the operators are warned of an imminent danger and can take action,
given that the general structure of said junction device includes a
plurality of bodies and flanges that are secured to one another in
reversible manner.
[0064] In an advantageous embodiment, said top surface portion of
the first flange and said bottom surface of the second forged body,
and where appropriate said bottom surface of the second flange, are
all plane annular surfaces.
[0065] In a preferred embodiment of the invention, said outer
casing of the float is secured to an internal second pipe of
greater diameter than said riser, said internal second pipe
preferably being a reinforced pipe of thickness greater than said
riser, and it includes a said second flange in the form of a body
of revolution to which the bottom end of said outer casing of the
float and the bottom end of said internal second pipe are secured,
preferably by welding, said second flange surrounding said second
forged body so that a second inner chamber is defined by an inner
surface of revolution of said second flange having the same axis of
revolution ZZ', by said top surface of revolution of said second
forged body), by the cylindrical outer surface of said top portion
of the riser and the cylindrical inner surface of said internal
second pipe, and by a closure flange at the top ends of said
internal second pipe and of said top portion of the riser, said
second chamber preferably co-operating with means for monitoring
the pressure inside said second chamber.
[0066] This embodiment makes it possible to monitor and reveal
leaks caused by cracking in the various components of the junction
device and the risers and pipes, or indeed mere failures to achieve
sealing, while still ensuring that the buoyancy of the float is
maintained.
[0067] Also preferably, said internal second pipe extends above
said float, preferably in the form of a reinforced pipe of
thickness greater than said riser which it surrounds, and
preferably a holding and guide device serves to guide said internal
second pipe relative to said floating support.
[0068] Furthermore, said reinforced internal pipe extends above
said riser and co-operates with the holding and guiding device so
as to take load off the top portion of the riser in its underwater
portion and in particular so as to avoid phenomena of said top
portion buckling as a result of the pressure and the temperature of
the fluid that it might be conveying.
[0069] According to the present invention the top end of the float
is secured to the top portion of the riser or of said internal
second pipe via a rigid junction.
[0070] In an advantageous embodiment, said float is a single float
extending over a length of 40 m to 100 m in order to confer
buoyancy enabling the entire bottom-to-surface connection to be
tensioned, said float preferably being made up of segments that are
assembled to one another, each constituted by a cylindrical box,
which boxes are preferably individually sealed, and secured
mechanically to one another in the longitudinal direction ZZ'.
[0071] Also advantageously, the buoyancy of said undersea pipe is
provided by said float without adding any additional tensioning
system that is secured to the floating support.
[0072] Installing the junction device of the invention with a
leaktight flexible joint at the bottom of the float does not
significantly alter the behavior of the connection device
concerning vibration phenomena of the pendulum-guitar type
described in WO/2001-53651, thereby advantageously eliminating the
appearance of such phenomena, providing the device of the invention
includes stabilizer means in the bottom portion of the float having
the effect of increasing the mass of water it entrains when it
moves, or lowering the center of gravity of the top portion of the
pipe in the vicinity of the float.
[0073] More particularly, the device of the invention includes
stabilizer means comprising a helical ramp surrounding said float
in its bottom portion close to its bottom end, and/or an additional
peripheral mass situated around the bottom portion of the
float.
[0074] Other characteristics and advantages of the present
invention appear in the light of the following detailed description
given with reference to the accompanying figures, in which:
[0075] FIG. 1 is a side view of a bottom-to-surface connection
device of the invention;
[0076] FIGS. 2 and 3 are section views through the bottom portion
of the float, showing the various components of a junction device
of the invention having a flexible leaktight joint;
[0077] FIGS. 4 and 5 are section views of two other embodiments of
a junction device of the present invention having a leaktight
flexible joint;
[0078] FIG. 6 is a section view through a device of the invention
as shown in FIG. 2, further including a drill string during a
well-drilling operation;
[0079] FIG. 7 is a section view of a device of the invention as
shown in FIG. 2, further including a second riser for safety
purposes having a production line installed therein;
[0080] FIG. 8 is a side view similar to FIG. 1, the
bottom-to-surface connection device being fitted with an additional
mass at the bottom of the float close to the junction device having
a leaktight flexible joint;
[0081] FIG. 9 is a side view similar to FIG. 1, in which the
bottom-to-surface connection device is fitted with anti-vortex fins
in the bottom portion of the box-type float close to the junction
device of the invention having a leaktight flexible joint;
[0082] FIG. 10 shows a variant of the connection between the first
laminated abutment and the first flange; and
[0083] FIG. 11 shows a variant embodiment with surfaces that are
frustoconical in shape.
[0084] FIG. 1 shows a bottom-to-surface connection device of the
invention comprising a riser 1 having a box-type float 2 made up of
segments 2.sub.1-2.sub.7 suitable for being handled on board a
barge or floating support 10 in order to be assembled, in
particular within a drilling bay 12, and thus building up a single
float. More precisely, the segments are constituted by cylindrical
boxes 2.sub.1-2.sub.7 each of which is individually hermetically
sealed, the boxes being mechanically secured to one another in the
longitudinal direction ZZ'. Said float 2 extends over a length of
40 m to 100 m in order to confer buoyancy that enables the entire
bottom-to-surface connection to be tensioned.
[0085] The float 2 is thus constituted overall by a can presenting
an essentially cylindrical casing 20 disposed coaxially around the
top portion 1b of the riser 1, at the underwater top end of the
pipe 1. The riser opens out at the surface inside a drilling bay 2
of a floating support or barge 10 that supports processing
equipment 11. The bottom portion 1a of the riser 1 that extends
below the float 2 is of substantially constant diameter down to the
sea bottom.
[0086] The top portion 1b of the riser above the float 2 is
surrounded by a reinforced pipe 3 secured to said float 2. Thus, it
is said reinforced pipe 3 that is held and guided by a guide system
comprising a known roller device 4 secured to a structure 6
connecting it to said barge 10. The guide device 4 allows the
reinforced pipe 3 to slide, and thus allows said riser to slide
along its longitudinal axis, and it guides it lateral movements in
a horizontal plane perpendicular to said longitudinal axis ZZ' of
the riser 1.
[0087] In FIG. 1, there is shown diagrammatically a junction device
8 creating a leaktight flexible joint between the bottom end of the
float 2 and said riser 1. The top end of the float 2 is secured to
said reinforced pipe 3 via a rigid junction 81.
[0088] FIGS. 2 and 3 show a preferred embodiment of a junction
device 8 of the invention having a leaktight and flexible
joint.
[0089] The junction device 8 of the invention is interposed between
a bottom portion 1a of the riser going down to the sea bottom and a
top portion 1b of the riser passing through the float 2 and rising
to the surface.
[0090] The term "shape of spherical section centered on
.largecircle." is used below to mean a shape that can be inscribed
in a casing of spherical section constituted by a surface of
revolution defined between two parallel horizontal section planes
and situated in the same hemisphere of a sphere of center
.largecircle., said center .largecircle. being placed above said
parallel horizontal section planes.
[0091] The junction device 8 in FIGS. 2 and 3 comprises:
[0092] a first forged body of revolution 22 having its bottom end
secured by welding 22a to the top end of the bottom portion 1a of
the riser, this first forged body of revolution 22 forming an
internal tubular duct section 22.sub.3 having substantially the
same diameter as the said bottom portion 1a of the riser to which
it is secured by a complete peripheral weld 22a; said first forged
body 22 presents in its top portion a flared shape forming a convex
outer first surface of revolution 22.sub.1 in the shape of a
spherical section centered on a point .largecircle. situated
substantially on the longitudinal axis ZZ' of said riser, and a
concave inner second surface of revolution 22.sub.2 in the shape of
a spherical section of diameter greater than the inside diameter of
the riser 1 and of diameter smaller than said convex outer surface
of revolution 22.sub.1, and substantially centered on the same
point .largecircle.;
[0093] a second forged body of revolution 24 whose top end is
welded at 24a over its entire periphery to the bottom end of said
top portion 1b of the riser, said second forged body of revolution
24 forming an internal tubular duct section 24.sub.4 of
substantially the same diameter as said top portion 1b of the
riser; said second forged body of revolution 24 further presenting
in its bottom portion a bottom first surface 24.sub.1 comprising a
plane annular portion, and a convex outer second surface 24.sub.3
in the shape of a spherical section of diameter smaller than that
of said spherical section of said concave internal surface
22.sub.2, substantially centered on the same point .largecircle. as
said other spherical section surfaces 22.sub.1, 22.sub.2, said
convex outer second surface 24.sub.3 being situated at a level
below said bottom first surface 24.sub.1 and constituting the
bottom end of the outer surface of said second forge body 24;
[0094] a first flange 23 in the form of a body of revolution
presenting a concave internal first surface 23.sub.1 of revolution
of spherical section substantially centered on the same point
.largecircle. as said other spherical section surfaces 22.sub.1,
22.sub.2, and 24.sub.3, and said first flange 23 also presents an
annular plane top surface 23.sub.2; and
[0095] a second flange 21 in the form of a body of revolution
having an annular plane bottom surface 21.sub.2 together with an
annular plane top outer surface 21.sub.1 and an inner surface of
revolution 21.sub.3.
[0096] Said second flange 21 in the form of a body of revolution
provides a connection between the bottom end of the cylindrical
outer casing 20 of the float 2 and an internal pipe 3 in said float
that contains said top portion 1b of the riser coaxially therein.
Said internal pipe 3 is a reinforced pipe of greater diameter and
greater thickness than the riser 1 and it is extended at its top
end to protect the riser 1 in the vicinity of the holder and guide
device 4 in the drilling bay 12. Said second flange 21 is secured
to the bottom end of the outer casing 20 by a peripheral weld 21b
and to the bottom end of said internal pipe 3 by a peripheral weld
21a. Said second flange 21 surrounds said second forged body
24.
[0097] The various forged bodies 22 & 24 and flanges 21 &
23 are assembled together and they co-operate as follows in order
to provide a junction device having a leaktight and flexible
joint:
[0098] said concave inner first surface 231 of the first flange 23
and said convex outer first surface 22.sub.1 of the first forged
body 22 co-operate elastically and in leaktight manner via a first
laminated abutment 30 in the form of a body of revolution in the
shape of a spherical section centered substantially on the same
point .largecircle., comprising a plurality of layers of elastomer
sandwiched between reinforcement of steel sheets with end sheets
bonded to said concave inner first surface 23.sub.1 and said convex
outer first surface 22.sub.1, thus providing a direct connection
comprising a leaktight and flexible joint between said first flange
23 and said first forged body 22;
[0099] said annular plane top surface 23.sub.2 of the first flange
23 is secured in leaktight and reversible manner to the plane
portion of the bottom surface 24.sub.1 of the second forged body 24
by bolting in holes 27 in said first flanges 23 and forged bodies
24, with sealing being provided by interposed O-rings 28;
[0100] said plane top surface 23.sub.2 of said first flange 23 is
likewise secured in leaktight and reversible manner to the annular
plane bottom surface 21.sub.2 of said second flange 21 by bolting
in holes 25 in said first and second flanges 21 and 23, with
sealing being provided by O-rings 28 interposed between said
surfaces 23.sub.2 and 24.sub.1; and
[0101] said concave inner second surface of revolution 22.sub.2 in
the shape of a spherical section of said first forged body 22 is
connected to said concave outer second surface 24.sub.3 of said
second forged body 24 via a second laminated abutment 31 in the
form of a body of revolution constituted by a plurality of layers
of elastomer sandwiched between rigid reinforcements of steel
sheet, the end reinforcements being bonded to said convex outer
second surface 24.sub.3 and to said concave inner surface 22.sub.2,
thus providing a direct, flexible, and leaktight connection between
the two forged bodies 22 and 24.
[0102] Laminated abutments made up of layers of elastomer and rigid
reinforcement are well known to the person skilled in the art.
[0103] It will be understood that said concave and convex surfaces
of spherical section have their concave sides facing upwards and
their convex sides facing downwards, i.e. they can be inscribed in
a hemisphere having a bottom horizontal section.
[0104] In FIGS. 2 and 3, a first leaktight internal chamber 40 is
defined by the top margin 22.sub.4 of said first forged body 22 and
the sides of said first and second laminated abutments 30 and 31
and the free portions of the bottom surfaces 24.sub.1 of the second
forged body 24, said concave inner first surface of revolution
23.sub.1 of the first flange 23, and said convex outer second
surface of revolution 24.sub.3 of the second forged body 24. The
chamber 40 is fitted with pressure monitoring means, e.g. an
external pressure gauge 42 connected to the chamber 40 via a duct
41 passing through the flange 23, or a pressure sensor connected to
the control cabin of the barge.
[0105] A second leaktight chamber 45 is defined by the top closure
flange 5, the cylindrical outer surface 1.sub.1 of the top portion
1b of the riser, the cylindrical inside surface 3.sub.1 of the
reinforced internal pipe 3, and the inner surface of revolution 213
of the second flange 21 and the top outer surface 24.sub.2 of the
second forged body 24. The second chamber 45 also co-operates with
an external pressure sensor or gauge connected to said chamber via
a duct 48 passing through the flange 21.
[0106] During movements of the float 2 associated with the riser 1,
due to swell or to current, the jointed connection device 8 between
the float and the riser allows a certain amount of pivoting to take
place, while keeping the bottom portion 1a of the riser under
tension. The spherical shape of said first and second laminated
abutments 30 and 31 has an automatic centering effect, and the
entire tensioning force created by the float (which might displace
500 tonnes) is transferred to the riser merely by said laminated
abutments being deformed in compression.
[0107] The second laminated abutment 31 acts mainly as a primary
seal, with the major fraction of vertical load transfer taking
place via the first laminated abutment 30.
[0108] Said reinforced pipe 3 at the top of the float 2 can be
assembled to an internal second pipe 3 inside the float, which
second pipe need not be reinforced, with assembly being implemented
in conventional manner using stiffeners, since the forces in this
zone are much smaller than in the bottom portion.
[0109] In a simplified version of the invention shown in detail in
FIG. 4, the second laminated abutment 31 providing primary sealing
as shown in FIG. 3 is omitted. The first laminated abutment 30 then
both provides primary sealing and also transfers vertical and
horizontal loads between the float and the riser. In this
simplified version, the pressure monitoring chamber 40 of FIGS. 2
and 3 no longer exists, and it is therefore not possible to detect
leaks therein.
[0110] In another simplified version of the invention shown in
detail in FIG. 5, the second forged body 24 and the second flange
21 of FIGS. 2 and 3 are combined in a single forged body 24 having
the bottom end of the outer casing 20 of the float 27 and the
bottom end of the riser 1b welded directly to its top surface
24.sub.2 at 24b; in this configuration there is no longer an
internal second pipe 3 surrounding said top portion 1b of the riser
1 coaxially. In this simplified version, the pressure monitoring
chamber 45 of FIGS. 2 and 3 no longer exists, and it is therefore
not possible in simple manner to detect locally any leaks from the
riser in this zone.
[0111] FIG. 3 shows the assembly inclined at an angle of value a
between the top portion 1b and the bottom portion 1a of the
riser.
[0112] In the descriptions of FIGS. 2 to 4, the laminated abutments
as described as being spherical and as co-operating with the
spherical bearing surfaces of the forged and machined flanges and
bodies 22, 23, and 24, the set of spheres and spherical bearing
surfaces then being described as having a common centers
.largecircle..
[0113] In fact, when fabricating those elements, it can be
considered that the point .largecircle. is indeed common to each of
the above-described spherical bearing surfaces; however, during
installation on site, the laminated abutments are subjected to
considerable forces, which may reach or exceed 500 tonnes, so they
deform in very significant manner, e.g. by a few centimeters, and
consequently the reference centers .largecircle. of some of the
components moves vertically relative to the reference centers of
other components. Nevertheless, it can be considered that in fact
the reference centers of the various spherical bearing surfaces
remain substantially centered at the common point .largecircle..
Similarly, during tilting through an angle .alpha., as shown in
FIG. 3, the various reference points of the spherical bearing
surfaces are shifted sideways a little, but nevertheless remain
substantially centered on .largecircle..
[0114] FIG. 6 shows the device of the invention during a
"single-casing" drilling operation. A string of rods 50 with a
drilling tool installed at its bottom end is set into rotation.
Drilling mud is injected under pressure inside the drill string 51,
and then rises together with drilling debris up the annular space
52 between the riser 1 and the drill string 50.
[0115] FIG. 7 shows a "double-casing" variant. Inside the riser 1,
there is advantageously installed a safety pipe 55 made up of unit
lengths that are connected to one another end-to-end by screw
fastening. A production line or drill string 50 is situated inside
this additional casing.
[0116] In this configuration, during drilling operations, mud
carrying drilling debris rises to the surface inside said safety
pipe 55 and therefore does not come into contact with the riser 1,
nor with the laminated abutment 31. This second casing constitutes
a primary barrier in the event of pressure rising due to the well
erupting or to any other accident, the riser 1 then constituting
the outer barrier that serves mainly to withstand the outside
pressure due to sea water, and also to the traction exerted by the
tensioning buoys. This disposition enables the safety of the
installation to be increased considerably, but it presents the
drawbacks of increasing its overall weight, which needs to be
compensated by increasing the total buoyancy volume.
[0117] In FIGS. 6 and 7, the drill strings 50 and the additional
casing 55 are continuous through the flexible joint zone situated
at the bottom portion of the float. Pivoting through the angle
.alpha. at the bottom of the float, as shown in FIG. 3, takes place
through very small angles, of the order of 2.degree. to 4.degree.
at the most, and said drill strings 50 and additional casing 55 can
take up the necessary curvature without unacceptable stresses
because of the clearance that exists relative to the riser 1, given
that they are of much smaller diameter.
[0118] Including a leaktight joint 8 at the bottom of the float
does not significantly modify the overall behavior of the assembly
with respect to vibration phenomena of the pendulum-guitar type as
described in patent WO/2001-53651 in the name of the Applicant, and
the appearance of such phenomena is advantageously eliminated by
installing as close as possible to said joint either an added
peripheral weight 60 situated around the bottom portion of the
float 2 as shown in FIG. 8, or antivortex type fins 61 providing a
helical ramp 61 surrounding said float 2 in its bottom portion
2.sub.7 close to its bottom end, as shown in FIG. 9.
[0119] By way of illustration, the dimensions of a junction device
8 of the invention can be as follows:
[0120] between the bottom end of the first forged body 22 and the
top end of the second forged body 24 the distance is about 60
centimeters (cm);
[0121] the inside diameter of the riser 1 is about 400 millimeters
(mm);
[0122] the outside diameter of said first and second flanges 21 and
23 is about 140 cm; and
[0123] the nominal diameter of the mean sphere corresponding to the
first leaktight abutment 30 is about 70 cm to 90 cm and its
thickness is 6 cm to 15 cm depending on the load to be transmitted
and the pivot angle .alpha..
[0124] In order to simplify fabrication of the first laminated
abutment 30, the flange 23 is advantageously made as two portions
23a and 23b as shown in FIG. 10. An Q-ring 23c provides sealing
between the two portions. The laminated abutments and the surfaces
of the various flanges form bodies and surfaces of revolution that
are defined as being spheres of center .largecircle., however it
remains within the spirit of the invention if conical shapes are
used, as shown in FIG. 11.
[0125] FIG. 11 shows a variant embodiment with the surfaces of
spherical shape replaced by surfaces of frustoconical shape.
[0126] In the right-hand side of FIG. 11, the apexes of said cones
converge substantially on a single point C, with the cones then all
being different from one another since the angle at the apex .beta.
varies from one cone to another.
[0127] In the left-hand side of the same FIG. 11, said cones all
have the same angle of the apex .beta. and they are therefore all
identical, with the apexes of the various cones then being
distributed substantially around the axis ZZ'.
[0128] Nevertheless, it is preferred to use shapes that are
spherical, since with conical shapes, when the joint takes on a
large angle .alpha., the laminated abutments can become pinched and
then cease operating in uniform manner.
[0129] Said first and second laminated abutments 30 and 31 can
accommodate bending through an angle .alpha. relative to said
longitudinal axis ZZ' having a value lying in the range 0 to
5.degree., and more usually 0 to 2.degree..
[0130] The junction device 8 of the present invention can be
manufactured and put into place using the following sequence:
[0131] 1) a first layer of uncured elastomer or a first rigid
reinforcement, preferably made of metal, is bonded to said inner
first surface 23.sub.1 of said first flange 23;
[0132] 2) the various layers of non-cured elastomer and of rigid
reinforcement making up said first laminated abutment 30 are
installed and bonded in succession;
[0133] 3) said first forged body 22 is put into place, being bonded
via its said outer surface 21 to the last layer or last rigid
reinforcement of said first laminated abutment 30;
[0134] 4) at least one O-ring 28 is put into place on a said top
surface of revolution 23.sub.2 of said first flange 23;
[0135] 5) said second forged body 24 is put into place causing it
to rest via its said plane bottom surface 241 on said top surface
of revolution 23.sub.2 of said first flange 23;
[0136] 6) where appropriate, a first elastomer layer or rigid
reinforcement is installed and bonded on said inner second surface
22.sub.2 of said first forged body 22 and then the various layers
of non-cured elastomer and the various rigid reinforcements of said
second laminated abutment 31 are installed in succession;
[0137] 7) said second forged body 24 is bonded via its said outer
second surface 24.sub.3 onto the last layer or reinforcement of
said second laminated abutment 31;
[0138] 8) said first flange and said second forged body 24 are
united by bolting;
[0139] 9) the assembly is heated in an oven to cure the various
layers of elastomer;
[0140] 10) the riser portions 1a and 1b are assembled together in
conventional manner by being welded to the respective forged bodies
22 and 24; and then
[0141] 11) the bottom end of the casing of the last float 20 is
welded to the top surface 24.sub.2 of the second forged body 24 or
to a top surface 21.sub.1 of a second flange 21, said flange having
a bottom surface 21.sub.2, itself bolted to a peripheral portion of
said top surface 23.sub.2 of said first flange 23 after initially
installing at least one O-ring 26 between the two surfaces.
[0142] When using frustoconical laminated abutments, i.e. having
metal reinforcement and elastomer layers that are frustoconical in
shape, these are easier to make since the surface can be developed
on a plane, which is not true of other shapes whether they be
elliptical, spherical, parabolic, or hyperbolic, which other shapes
require precision stamping operations that are more difficult to
perform.
[0143] In an advantageous embodiment that facilitates installing
and assembling the junction device 8 of the invention, said first
flange 23 comprises two portions 23a and 23b, in which the first
portion 23a is a body of revolution including said inner first
surface 23.sub.1, and said second portion 23b is a peripheral
flange comprising said top surface 23.sub.2, said second portion
23b being secured in leaktight and reversible manner to said first
portion 23a via at least one O-ring 29 by securing said top surface
portion 23.sub.2 of the first flange 23 in leaktight and reversible
manner to said bottom surface 24.sub.1 of said second forged body
24.
[0144] In an advantageous embodiment, the junction device 8 is put
into place and manufactured by bonding said first laminated
abutment 30 onto a first portion 23a of said first flange 23, said
first portion 23a being a body of revolution including an inner
surface corresponding to said inner first surface of revolution
23.sub.1.
[0145] The following assembly steps are then performed:
[0146] 1) said first laminated abutment 30 is bonded to said body
of revolution 23a;
[0147] 2) the first forged body 22 is bonded via its said outer
surface 22.sub.1 to the free face of said laminated abutment
30;
[0148] 3) said second laminated abutment 31 is bonded to said inner
second surface 22.sub.2 of the first forged body 22;
[0149] 4) said outer second surface of revolution 24.sub.3 of the
second forged body 24 is bonded to the free face of said second
laminated abutment 31;
[0150] 5) the assembly is put into an oven in order to cure the
various layers of elastomer; and then
[0151] 6) a second portion 23b of said first flange 23 comprising
both said top surface portion 23.sub.2 co-operating in leaktight
manner via an O-ring 28 with said bottom surface 24.sub.1 of the
second forged body 24, and also a concave surface 23c capable of
co-operating with the free outer face of said first portion 23a via
an O-ring 29 is bolted to the second forged body 24, and where
appropriate to a said second flange 21, the first portion 23a of
the first flange 23 thus also being prevented from moving and the
entire junction device 8 thus being united.
[0152] The advantage of this embodiment is that it makes it
possible to verify that the layers constituting the edges 30a and
31a of said first and second laminated abutments 30 and 31 have
been properly cured.
[0153] The forged bodies 22 and 24 and the flanges 21 and 23 are
described as being bodies of revolution, however it would remain
the spirit of the invention for those parts to present external
shapes that are polygonal or irregular, it-is only the surfaces
23.sub.1, 22.sub.1, 22.sub.2, and 24.sub.3 which receive the
laminated abutments that need to be substantially spherical about a
center .largecircle., or ellipsoidal, or indeed conical, as
described above.
* * * * *